<big><b>Five things to watch: 49ers (1-0) at Seahawks (1-0)</b> (Week 2)</big>
<small>Sunday, Sept. 15 | 5:30 p.m. PDT | CenturyLink Field, Seattle | TV: NBC</small>
On Sunday, the San Francisco 49ers roll into CenturyLink Field for a heated rivalry game with big implications. It's the most anticipated game (so far) of the most anticipated season in Seahawks history, and tensions have been building for months. As the teams and fans alike prepare for a wild night Sunday, here are five of the biggest things to keep an eye on as the Seahawks battle the Niners on ''Sunday Night Football.'' The whole nation will be watching. less

But first ... <b>the last they met:</b>
At the end of last season, the Seahawks were on a hot streak after blowing out the Cardinals and Bills, and the stakes were high for the 49ers matchup: San Francisco was leading the NFC West and Seattle needed a win to clinch a Wild Card playoff berth. Fans were worried the mighty 49ers would come into CenturyLink Field on Dec. 23 and beat down the streaking Seahawks -- as it turned out, the opposite happened.
The Hawks put up 14 quick points but the Niners looked to be surging back in the second quarter, driving all the way to Seattle's 3-yard line. But the defense stopped them there, and when S.F. kicker David Akers tried for a 21-yard field goal, Red Bryant blocked it and Richard Sherman ran it all the way to the other end for a touchdown. With a 21-0 lead, the Seahawks had stolen all the momentum. Russell Wilson threw for 171 yards and four touchdowns, and Marshawn Lynch rushed for 111 yards and one score on the ground, as the Seahawks walloped the 49ers 42-13 just before Christmas. less

But first ... <b>the last they met:</b>
At the end of last season, the Seahawks were on a hot streak after blowing out the Cardinals and Bills, and the stakes were high for the 49ers matchup: San Francisco ... more

Photo: Otto Greule Jr / Getty Images

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<b>1. Seattle's weak O-line v. S.F.'s strong defense</b>
Last week against Carolina, Seahawks quarterback Russell Wilson spent a lot of time avoiding pressure, scrambling out of the pocket and doing what he does best: squirting out of the hands of guys hungry for a sack. It wasn't a good outing by Seattle's offensive line, and the team's weakness and lack of depth there has already become worrisome. The Panthers held Seattle to just 60 rushing yards, yet Wilson was able to compensate and threw for 320 yards and a touchdown. The Hawks escaped with a hard-fought 12-7 victory.
This Sunday, the O-line will be facing a formidable San Francisco defense that currently ranks sixth in the NFL against the run; Seattle's big uglies could have their hands full. Perhaps the weakest link on the O-line is right guard J.R. Sweezy, who converted from a defender in college and beat out John Moffitt for the starting job this preseason. Behind Sweezy and his right-side counterpart, Paul McQuistan, on the depth chart is former fist-round draft pick James Carpenter, who is looking to assert himself after two seasons marred by knee injuries. Right tackle Breno Giacomini has also struggled protecting Wilson, so watch to see whether the O-line can contain guys like Niners linebacker Aldon Smith, who led the team with 19.5 sacks last season on his way to the Pro Bowl and All-Pro first team.
That said, the 49ers' secondary did allow Green Bay quarterback Aaron Rodgers to throw for 333 yards and three touchdowns last weekend. Seattle could find more success through the air than on the ground Sunday. less

<b>1. Seattle's weak O-line v. S.F.'s strong defense</b>
Last week against Carolina, Seahawks quarterback Russell Wilson spent a lot of time avoiding pressure, scrambling out of the pocket and doing what he ... more

Photo: Streeter Lecka / Getty Images

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<b>2. The productivity of Marshawn Lynch</b>
While we're on the topic, let's talk about Seattle's running game. Last weekend, starting running back Marshawn Lynch managed just 43 yards on 17 carries against the Panthers, as Seattle's offensive line struggled to open up running lanes. Backup Robert Turbin added just 17 yards more on three carries, including the Seahawks' longest run (a 15-yarder) of the game. Despite the subpar performance for the team that ran the most rushing plays in the NFL last season, QB Russell Wilson was able to adjust and get it done through the air.
As we just mentioned, Lynch's productivity Sunday will depend largely on the strength of Seattle's offensive line -- arguably the team's weakest positional group. We know what Lynch can do -- last season he ran for 1,590 yards -- but we have yet to see what the 49ers will allow him to do. Standing in his way will be All-Pro linebacker Aldon Smith, who had 19.5 sacks last season and clearly has a knack for breaking through into the backfield. The Niners ranked as the NFL's second-best defense last year (behind the Seahawks), and were suffocating against both the run and the pass. We expect no different this year. less

<b>2. The productivity of Marshawn Lynch</b>
While we're on the topic, let's talk about Seattle's running game. Last weekend, starting running back Marshawn Lynch managed just 43 yards on 17 carries against ... more

Photo: Streeter Lecka / Getty Images

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<b>3. The defense against Colin Kaepernick</b>
Last year, the Seahawks finished with the NFL's best defense, giving up the fewest points (245) of any team through the season. This year's defensive squad has the potential to be even better, particularly with the additions of pass-rushers Cliff Avril and Michael Bennett to an already sack-happy duo of Chris Clemons and Bruce Irvin. Problem is, at this point, not all of them are playing. Avril is slated to return after a preseason hamstring injury, but Clemons is expected to sit out Sunday's game again and Irvin is still suspended. Nevertheless, Seattle's defense did hold Panthers QB Cam Newton last weekend to his lowest passing game (125 yards) since he joined the NFL, and hasn't given up more than 10 points a game since the beginning of the preseason.
On Sunday, however, Seattle's defense will have to deal with another dynamic quarterback in S.F.'s Colin Kaepernick. We've all heard how much of a sensation he is, jumping into the starting role midway through 2012 and leading the 49ers to the Super Bowl. Kaepernick is dangerous both with his arm and his legs, able to hit a streaking receiver or take the ball himself. That makes it even harder to defend against powerful running back Frank Gore, who rushed for 1,214 yards last season but was held to just 44 against Green Bay. Kaepernick threw for a whopping 412 yards against the Packers last weekend -- the Seahawks are hoping to prevent a repeat performance. less

<b>3. The defense against Colin Kaepernick</b>
Last year, the Seahawks finished with the NFL's best defense, giving up the fewest points (245) of any team through the season. This year's defensive squad has ... more

Photo: Steve Dykes / Getty Images

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<b>4. Anquan Boldin v. the 'Legion of Boom'</b>
One of the biggest takeaways from San Francisco's skin-of-the-teeth 34-28 victory over the Packers last Sunday was the emergence of another potentially dominant NFL passing duo: Colin Kaepernick and Anquan Boldin. When the 49ers lost star receiver Michael Crabtree to <del>free agency</del> injury this offseason, and facing a divisional rival in Seattle that had just acquired Percy Harvin, they traded a sixth-round draft pick to the Ravens for Boldin. Some wondered how well the 10-year veteran would fit into San Francisco's scheme, but the Packers win last Sunday answered that question soundly: extremely well. Kaepernick hit Bolden 13 times for 208 yards and a touchdown.
But the Packers didn't have Seattle's lights-out secondary, famously nicknamed the ''Legion of Boom.'' Boldin will be going up against cornerback Richard Sherman for sure, but likely won't have to deal with Brandon Browner, who is doubtful for Sunday with a hamstring injury. Rounding out the legion are safeties Earl Thomas and Kam Chancellor, who both had great outings last week at Carolina -- particularly Thomas, who was named All-Pro in 2012. Filling in behind them all on the depth chart are corners Byron Maxwell, Walter Thurmond and Jeremy Lane, and safeties Jeron Johnson and Chris Maragos.
''I'll just have to knock the ball down,'' Sherman said Thursday of defending Boldin. ''There's some give-and-take in there -- with a physical receiver like him there's always going to be some give-and-take. He's going to be pushing you and grabbing you. It's going to be a physical battle, so you have to prepare you mind and your body for that type of game. Because if you're not prepared for that, then he'll dominate like he did (versus Green Bay)." less

<b>4. Anquan Boldin v. the 'Legion of Boom'</b>
One of the biggest takeaways from San Francisco's skin-of-the-teeth 34-28 victory over the Packers last Sunday was the emergence of another potentially ... more

Photo: Thearon W. Henderson / Getty Images

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<b>5. Emotions and penalties</b>
The tension has been building for months and these teams do not like each other. San Francisco will be trying to avenge the 42-13 blowout in December; Seattle will be playing for NFC West and NFL dominance. Though most players have remained relatively tame in this week's lead-up to Sunday (besides 49ers running back Anthony Dixon's <a href='http://blog.seattlepi.com/football/2013/09/12/49ers-rb-anthony-dixon-prepring-to-play-seattle-she-hawks/'>''She-Hawks'' comment</a> and Seattle linebacker K.J. Wright's ''Forty-Whiners'' response), we expect the lid to blow off Sunday. The competition will be fierce, violent and possibly vicious. Just think <a href='http://www.youtube.com/watch?v=78qF72JwJwA'>Kam Chancellor's huge hit</a> in December on Vernon Davis.
Will we see any brawls? Possibly. But expect head coaches Pete Carroll and Jim Harbaugh to at least try to keep their players in check. Seattle has continued (since last season) to struggle with penalties, so the Seahawks should be careful to not get out of control. Personal fouls could be a decisive element of Sunday's contest. less

<b>5. Emotions and penalties</b>
The tension has been building for months and these teams do not like each other. San Francisco will be trying to avenge the 42-13 blowout in December; Seattle will be ... more

Photo: Otto Greule Jr / Getty Images

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<b>BONUS: Jim Harbaugh v. Pete Carroll</b>
The Seahawks-Niners rivalry is fairly young, but that doesn't make it any less intense. You can trace its origin to the head coaches, who faced each other not long ago as college rivals, Seattle's Pete Carroll at the helm of USC and San Francisco's Jim Harbaugh in charge at Stanford. In fact, you can trace the origin back to one game in 2009, when Harbaugh came into Los Angeles and ran up the score on Carroll's Trojans.
''Look at them all runnin' out,'' Harbaugh was caught on TV saying as he walked to meet Carroll at midfield, referring to the exiting Trojans. An unpleased Carroll asked, <a href='http://blog.seattlepi.com/football/2011/09/07/pete-carroll-and-jim-harbaugh-whats-your-deal-revisited/'>''What's your deal?''</a> Their public feud started then, and they brought with them it to the NFL. Though both would deny any dislike for the other, we know there's some bad blood between these two. Watch to see whether they have any fiery interaction Sunday. less

<b>BONUS: Jim Harbaugh v. Pete Carroll</b>
The Seahawks-Niners rivalry is fairly young, but that doesn't make it any less intense. You can trace its origin to the head coaches, who faced each other not long ... more

Photo: Michael Zagaris / Getty Images

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<b>BONUS 2: Guinness World Record for crowd roar</b>
Thought CenturyLink Field was loud already? Just wait until Sunday, when the 12th Man will be shooting to <a href='http://blog.seattlepi.com/football/2013/07/08/12th-man-shooting-for-crowd-roar-guinness-record-when-seahawks-host-49ers/'>break the Guinness World Record for loudest crowd roar</a>. A group of Seahawks fans organized the record attempt and Guinness is sending a representative to oversee. The record to beat is 131.76 decibels, set during a 2011 soccer match at the Ali Sami Yen Sport Complex Turk Telekom Arena in Istanbul, Turkey.
On their website, the Seahawks say Seattle's 12th Man has been measured at 112 decibels -- louder than a power saw or a rock concert, and not much quieter than a Boeing 747. On Sunday, fans will be making ear-splitting noise, measured by an official Guinness World Records ''adjudicator'' with a sound meter on the field. Directed by prompts on the stadium's big screens, fans will get -- at the most -- three attempts to break the record, and under Guinness rules can use their voices and any analog noisemakers but no electronically amplified sounds. A Guinness spokesperson said the 12th Man should know almost immediately whether they've accompolished the feat.
And, by the way, Colin Kaepernick struggled mightily with the 12th Man the last time he was at the CLink. less

<b>BONUS 2: Guinness World Record for crowd roar</b>
Thought CenturyLink Field was loud already? Just wait until Sunday, when the 12th Man will be shooting to <a ... more

Photo: Otto Greule Jr / Getty Images

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Five things to watch: San Francisco 49ers at Seattle Seahawks

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